When a golf club head strikes a golf ball, a force is seen on the club head at the point of impact. If the point of impact is aligned with the center face of the golf club head in an area of the club face typically called the sweet spot, then the force has minimal twisting or tumbling effect on the golf club. However, if the point of impact is not aligned with the center face, outside the sweet spot for example, then the force can cause the golf club head to twist around the center face. This twisting of the golf club head causes the golf ball to acquire spin. For example, if a typical right handed golfer hits the ball near the toe of the club this can cause the club to rotate clockwise when viewed from the top down. This in turn causes the golf ball to rotate counter-clockwise which will ultimately result in the golf ball curving to the left. This phenomenon is what is commonly referred to as “gear effect.”
Bulge and roll are golf club face properties that are generally used to compensate for this gear effect. The term “bulge” on a golf club typically refers to the rounded properties of the golf club face from the heel to the toe of the club face.
The term “roll” on a golf club typically refers to the rounded properties of the golf club face from the crown to the sole of the club face. When the club face hits the ball, the ball acquires some degree of backspin. Typically this spin varies more for shots hit below the center line of the club face than for shots hit above the center line of the club face.
FIG. 1 illustrates the problem to be solved by the present invention. FIG. 1 shows a ball location with respect to the intended target when the golf ball is struck with a club having a constant bulge and roll radius. The nine rectangles indicate the ball location when struck in the respective heel, toe, center, high, center, low combinations. The fairway 124 is separated from the rough 126 by a fairway edge 120,122. The final ball location is shown with respect to an intended target line 118. The intended target line 118 is the line along which the golf club head center is aimed when the golf is at the address position. When the golf ball is struck in the high position, the golf ball tends to have a “left tendency” which means the ball's final resting position will be left of the target line 118. As illustrated by points 100, 102, and 104 shown in FIG. 1. When the golf ball is struck in the low position, the golf ball tends to have a “right tendency” which means the ball's final resting position will likely be to the right of the target line 118 as illustrated by points 112, 114,116 shown in FIG. 1. When a golf ball impacts the ball in the central horizontal portion of the face, the ball tends to come to rest on target relative to the target line 118 as illustrated by points 106,108,110 shown in FIG. 1.
A golf club design is needed to counteract the left and right tendency that a player encounters when the ball impacts a high or low position on the club head striking face.
The problems noted above are equally applicable to iron-type golf clubs or “irons.” While all clubs in a golfer's bag are important, both scratch and novice golfers rely on the performance and feel of their irons for many commonly encountered playing situations.
Irons are generally configured in a set that includes clubs of varying loft, with shaft lengths and clubhead weights selected to maintain an approximately constant “swing weight” so that the golfer perceives a common “feel” or “balance” in swinging both the low irons and high irons in a set. The size of an iron's “sweet spot” is generally related to the size (i.e., surface area) of the iron's striking face, and iron sets are available with oversize club heads to provide a large sweet spot that is desirable to many golfers.
Conventional “blade” type irons have been largely displaced (especially for novice golfers) by so-called “perimeter weighted” irons, which include “cavity-back” and “hollow” iron designs. Cavity-back irons have a cavity directly behind the striking plate, which permits club head mass to be distributed about the perimeter of the striking plate, and such clubs tend to be more forgiving to off-center hits. Hollow irons have features similar to cavity-back irons, but the cavity is enclosed by a rear wall to form a hollow region behind the striking plate. Perimeter weighted, cavity back, and hollow iron designs permit club designers to redistribute club head mass to achieve intended playing characteristics associated with, for example, placement of club head center of gravity or a moment of inertia.
In addition, even with perimeter weighting, significant portions of the club head mass, such as the mass associated with the hosel, topline, or striking plate, are unavailable for redistribution. The striking plate must withstand repeated strikes both on the driving range and on the course, requiring significant strength for durability.
Golf club manufacturers are consistently attempting to design golf clubs that are easier to hit and offer golfers greater forgiveness when the ball is not struck directly upon the sweet spot of the striking face. As those skilled in the art will certainly appreciate, many designs have been developed and proposed for assisting golfers in learning and mastering the very difficult game of golf.
With regard to iron type club heads, cavity back club heads have been developed. Cavity back golf clubs shift the weight of the club head toward the outer perimeter of the club. By shifting the weight in this manner, the center of gravity of the club head is pushed toward the sole of the club head, thereby providing a club head that is easier to use in striking a golf ball. In addition, weight is shifted to the toe and heel of the club head, which helps to expand the sweet spot and assist the golfer when a ball is struck slightly off center.
Shifting weight to the sole lowers the center of gravity (CG) of the club resulting in a club that launches the ball more easily and with greater backspin. Golf club designers may measure the vertical CG of the golf club relative to the ground when the golf club is soled and in the proper address position, this CG measurement will be referred to as Zup or Z-up or CG Z-up. Decreasing Z-up as opposed to increasing it is preferable. Golf club designers can use a golf club with a low Z-up to design clubs for both low and high handicap golfers by either making a golf club that maintains similar launch angles but increases ball speed and distance or a club that launches the ball more easily in the air. Higher handicap golfers typically have trouble launching the ball in the air so a club that gets the ball in the air more easily is a great benefit. For lower handicap golfers, launching the ball in the air is not typically an issue. For lower handicap golfers, golf club designers may strengthen the loft of the golf club to maintain similar launch conditions and similar amounts of backspin, but resulting in greater ball speed and distance gains of several yards. The result is better golfers may now use one less club when approaching a green, such as, for example, a golfer may now use a 7-iron instead of a 6-iron to hit a green. Placing weight at the toe increases the moment of inertia (MOI) of the golf club resulting in a club that resists twisting and is thereby easier to hit straight even on mishits.
As club manufacturers have learned to assist golfers by shifting the center of gravity toward the sole of the club head, a wide variety of designs have been developed. Unfortunately, many of these designs substantially alter the appearance of the club head while attempting to shift the center of gravity toward the sole and perimeter of the club head. For example, one method of lowering the CG is to simply decrease the face height at the toe and make it closer in height to the face height at the heel of the club resulting in a very untraditional looking club. This is highly undesirable as golfers become familiar with a certain style of club head and alteration of that style often adversely affects their mental outlook when standing above a ball and aligning the club head with the ball. As such, a need exists for an improved club head which achieves the goal of shifting the center of gravity further toward the sole and perimeter of the club head without substantially altering the appearance of a traditional cavity back club head with which golfers have become comfortable. The present invention provides such a club head.
Unfortunately, an additional problem arises from relocating mass on a golf club in that the acoustical properties of the golf club head is often negatively impacted. The acoustical properties of golf club heads, e.g., the sound a golf club head generates upon impact with a golf ball, affect the overall feel of a golf club by providing instant auditory feedback to the user of the club. For example, the auditory feedback can affect the feel of the club by providing an indication as to how well the golf ball was struck by the club, thereby promoting user confidence in the club and himself.
The sound generated by a golf club is based on the rate, or frequency, at which the golf club head vibrates and the duration of the vibration upon impact with the golf ball. Generally, for iron-type golf clubs, a desired first mode frequency is generally around 3,000 Hz and preferably greater than 3,200 Hz. A frequency less than 3,000 Hz may result in negative auditory feedback and thus a golf club with an undesirable feel. Additionally, the duration of the first mode frequency is important because a longer duration results in a ringing sound and/or feel, which feels like a mishit or a shot that is not solid. This results in less confidence for the golfer even on well struck shots. Generally, for iron-type golf clubs, a desired first mode frequency duration is generally less than 10 ms and preferably less than 7 ms.
Accordingly, it would be desirable to reduce the topline weight to shift the CG to the sole and/or toe while maintaining acceptable vibration frequencies and durations. Such a club would be easier to hit because it would launch the ball more easily (low CG) and/or hit the ball straighter even on mishits (increased MOI), and the club would still provide desirable feel through positive auditory feedback. Accordingly, there exists a need for iron-type golf club heads with a strong and lightweight topline.
Golf clubs are typically manufactured with standard lie and loft angles. Some golfers prefer to modify the lie and loft angles of their golf clubs in order to improve the performance and consistency of their golf clubs and thereby improve their own performance.
In some cases, golf club heads, particularly iron-type golf club heads, can be adjusted by being plastically bent in a post-manufacturing process. In such a bending process, it can be difficult to plastically bend the material of the club head in a desired manner without adversely affecting the shape or integrity of the hosel bore, the striking face, or other parts of the club head. In addition, advancements in materials and manufacturing processes, such as extreme heat treatments, have resulted in club heads that are stronger and harder to bend and have more sensitive surface finishes. This increases the difficulty in accurately bending a club head in a desired manner without adversely affecting the club head. Additionally, the iron-type club heads must have a hosel design that will allow for bending. Bending bars are used for bending golf club heads to a golfer's preferred loft and lie. The bending process requires a significant amount of force and/or torque to plastically deform the iron-type club head. It can be difficult to plastically bend the club head in a desired manner without adversely affecting the shape or integrity of the hosel bore, the striking face, or other parts of the club head. As a result the hosel must have significant structural integrity to withstand multiple bending sessions and repeated strikes at the range and the golf course. The risk of club failure makes for a challenging design problem and makes the mass associated with the hosel largely unavailable for redistribution.
Accordingly, there exists a need for iron-type golf club heads with strong and lightweight hosels, centers of gravity shifted toward the sole, and/or a strong lightweight topline that can counteract the left and right tendency that a player encounters when the ball impacts a high or low position on the club head striking face.